Intermittent web drive mechanism employing unidirectional clutches

ABSTRACT

Means for intermittently advancing a web of flexible film comprising drive means for imparting repeating cycles of intermittent motion and dwell to a web of flexible film with the web motion normally being in only the forward direction. The drive means includes an output shaft having first and second input driver means coupled to the output shaft, with the driver means being arranged in phased relationship, one to another, so as to achieve motion in the output shaft for more than 180* of motion in the input shaft. The driver means are arranged in overlapped phased relationship, one to another, so as to achieve motion from each driver means for less than 180* of motion in the input shaft. Coupling means including first and second unidirectional clutch means such as a one way or overriding clutch are provided for intermittently inter-coupling the first driver means to the input and output shafts for initiating rotation of the output shaft, and for continuing the rotation for a predetermined motion segment of less than one-half cycle of rotation of the input shaft or until the rate of speed of the second driver means overtakes the rate of the first driver, at which point decoupling of the first driver means occurs, along with substantially simultaneous inter-coupling occurring between the second driver means and the input and output shafts for the continued rotation of the output shaft for a second predetermined motion segment of less than one-half cycle of rotation of the input shaft, at which point, de-coupling the second driver means occurs.

United tates ?atent [1 1 Monahan [4 1 May 20, 1975 1 INTERMITTENT WEBDRIVE MECHANISM EMPLOYING UNIDIRECTIONAL CLUTCl-IES [75] Inventor:Thomas J. Monahan, Swansea,

Mass.

[73] Assignee: G. T. Schjeldahl Company,

Northfield, Minn.

22 Filed: Apr. 10, 1973 21 Appl, No.: 349,778

[52] US. Cl 93/8 R; 74/121; 74/125.5; 156/515; 226/156; 93/33 H [51]Int. Cl ..B31b 1/10 [58] Field of Search...74/125.5; 120,121; 156/515;93/DIG. 1, 33 H, 8 R; 226/156, 226/157; 83/401, 436

Primary Examiner-Roy Lake Assistant Examiner.lames F. Coan [57] ABSTRACTMeans for intermittently advancing a web of flexible film comprisingdrive means for imparting repeating cycles of intermittent motion anddwell to a web of flexible film with the web motion normally being inonly the forward direction. The drive means includes an output shafthaving first and second input driver means coupled to the output shaft,with the driver means being arranged in phased relationship, one toanother, so as to achieve motion in the output shaft for more than 180of motion in the input shaft. The driver means are arranged inoverlapped phased relationship, one to another, so as to achieve motionfrom each driver means for less than 180 of motion in the input shaft.Coupling means including first and second unidirectional clutch meanssuch as a one way or overriding clutch are provided for intermittentlyintercoupling the first driver means to the input and output shafts forinitiating rotation of the output shaft, and for continuing the rotationfor a predetermined motion segment of less than one-half cycle ofrotation of the input shaft or until the rate of speed of the seconddriver means overtakes the rate of the first driver, at which pointdecoupling of the first driver means occurs, along with substantiallysimultaneous intercoupling occurring between the second driver means andthe input and output shafts for the continued rotation of the outputshaft for a second pre-determined motion segment of less than one-halfcycle of rotation of the input shaft, at which point, de-coupling thesecond driver means occurs.

9 Claims, 9 Drawing Figures SHEET 2 BF 3 PATENTED Z INTERMITTENT WEBDRIVE MECHANISM EMPLOYING UNIDHRECTIONAL CLUTCHES CROSS-REFERENCE TORELATED APPLICATION The present invention is an improvement over thatinvention disclosed and claimed in co-pending application Ser. No.151,842, filed June 10, 1971, entitled INTERMITTENT DRIVE MECHANISM, nowUS. Pat. No. 3,776,804 which application constituted a continuation inpart of application Ser. NO. 81369, filed Oct. 16, 1970, also entitledINTERMITTENT DRIVE MECHANISM, now abandoned, both applications beingassigned to the same assignee as the present invention, and in which Iam named as co-inventor.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates generally to apparatus for intermittently advancing aweb of flexible film, and more specifically to drive means in phasedrelationship, one to another, employing unidirectional clutch means forindependently imparting repeating cycles of intermittent motion followedby a dwell cycle to a web of flexible film, the drive means beingoperated in synchronism with a sealing apparatus which performs anoperation on the web, such as, for example, the simultaneous welding andsevering ofa pair of superimposed webs so as to form a side-weld bagstructure or the like.

2. Description of the Prior Art The apparatus of the present inventionconstitutes an improvement over those devices disclosed and claimed inU.S. Pat. No. 2,947,345, G. T. Schjeldahl, Machine for Making Articlesfrom Multiple Thermoplastic Webs dated Aug. 2, 1960; and US. Pat. No.2,997,889, G. T. Schjeldahl, et al., Intermittent Engine, dated Aug. 29,1961, both of these patents being assigned to the same assignee as thepresent invention.

In each of these prior patents, apparatus is described for the handlingof thermoplastic webs, particularly superimposed thermoplastic webswhich are treated with a hot-knife performing a simultaneous severingand welding operation on the webs. Each of the devices described inthese patents utilizesrack-and-pinion drives for the intermittentactuation of the draw rolls. The apparatus of the present invention alsoutilizes a rackand-pinion mechanism, the arrangement being modified soas to extend the draw cycle beyond the 180 of machine motion whichconstituted the maximum previously available with a conventionalrack-and-pinion drive.

Machine speed is normally limited by the draw cycle, since thedurability of the film being treated will determine the maximumacceleration rate possible in the Web. Inasmuch as the apparatus of thepresent invention provides an extended draw cycle, it is possible toincrease the cycle rate of the apparatus without increasing the rate ofacceleration of the draw mechanism, thus providing an increased rate ofproduction over that which would be possible with apparatus equippedwith conventional drive mechanisms.

SUMMARY OF THE INVENTION In accordance with the present invention, drivemeans are provided for imparting repeating cycles of intermittent motionand dwell to a web of flexible film, with the motion normally beingimparted to the system with a pair of rack-and-pinion drives. The rackis coupled to an input shaft, with the teeth of the rack being in meshwith a pinion on an output shaft. The individual racks are preferablycoupled through means associated with opposite ends of a draw roll, andare arranged in arcuately spaced phased relationship. In order toachieve proper relative motion between the phased racks, unidirectionalclutch means, such as a one way or overriding clutch is used between thepinion and the shaft, thereby rendering it possible for automaticshifting of drives to occur. Thus, the first rack will apply initialforward motion to the system, with the second rack taking over when itsrate of speed exceeds that of the first rack. In a typical situation,the individual eccentric arms driving the racks may be displaced for ofarc, with the first rack driving the output shaft for of motion. Uponachieving 90 of motion, the first rack decelerates and the arcuate rateof speed of the second rack overtakes that of the first and drives theoutput shaft at that point in the cycle. Since the second rack will, atthat time, be advanced 30 from its individual starting point, it willcontinue driving the output shaft for an additional 150 of motion. Atthat point, the input shaft has rotated 300 and the remaining 60 areavailable for the dwell cycle.

Therefore, it is the principal object of the present invention toprovide an improved drive means employing unidirectional clutches foruse in imparting repeating cycles of intermittent motion and dwell to aweb of flexible film, the drive means utilizing rack-and-pinionstructures and being capable of imparting motion to the web for morethan 180 of machine operation.

It is yet a further object of the present invention to provide meansforintermittently advancing a web of flexible film utilizingunidirectional clutches with twin rack-and-pinion drives, the individualracks being disposed in spaced phased relationship one to another, so asto impart motion to the web over more than 180 of input shaft rotation.

It is still a further object of the present invention to provide animproved bag-making machine utilizing drive means for intermittentlyadvancing superimposed webs of thermoplastic sheetfilm, the drive meansutilizing twin rack-and-pinion drives, with the racks being coupled to acommon input shaft and being disposed in spaced-apart phasedrelationship so as to achieve drive cycles in excess of 180 of rotationof the input shaft.

Other and further objects of the present invention will become apparentto those skilled in the art upon a study of the following specification,appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view ofthe rack-andpinion drive means employed in the present invention, andillustrating in solid lines, a rack-and-pinion assembly together withits unidirectional clutch on the near side of the apparatus, andillustrating, in phantom, the identical rack structure on the oppositeside of the structure;

FIG. 2 is an end elevational view of the structure and illustrating thearrangement and disposition of the twin rack drives and unidirectionalclutch, each of which is coupled to one end of the draw roll;

FIG. 3 is a plot of rotation of the input shaft versus draw rate for atypical operational cycle in one operational mode, and illustrating theactive portion of the draw for the individual drivers in solid line, andillustrating idle portions for the individual driver mechanisms indashed lines;

FIGS. 40 and 4b are schematic illustrations of the rack-and-pinionstructures taken from opposite sides of the machines, and illustratingthe spaced phase relationship existing between the individual rackstructures, with FIG. 4a illustrating the rack and unidirectional clutchon one side of the structure at the start of its draw cycle, and withFIG. 4b illustrating the disposition of the rack on the opposite side ofthe structure in the disposition where its draw cycle is initiated after120 rotation of the driver shaft;

FIG. 5 is a partial vertical sectional view of the rackand-pinionstructure shown in FIG. 1, and illustrating this portion of theapparatus in greater detail, this view being taken generally along theline and in the direction of the arrows 5-5 of FIG. 1;

FIG. 6 is a view similar to FIG. 1, and additionally illustrating thedetails of the reciprocating hot-knife structure employed in abag-making machine utilizing the drive mechanism of the presentinvention;

FIG. 7 is a partial vertical sectional view taken through the centeraxis of the apparatus, and illustrating details of the draw roll andsealing sections of the apparatus; and

FIG. 8 is a detail view showing the arrangement of the overriding clutchas it is mounted with relationship to the draw roll.

DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the preferredmodification of the present invention, the bag-making apparatusgenerally designated 10 is provided with a frame structure including abase 11, and upright frame mounting mem bers 12, 13, 14, l5, l6 and 17.Details of a conventional bag-making machine utilizing a conventionaldrive are set forth in US. Pat. No. 2,947,345, as referred tohereinabove. A drive motor is mounted on the base member 11 byconventional means, the shaft of motor 20 being coupled at 21 to driveshaft 22, shaft 22 being coupled to the input of a conventionalclutchbrake assembly generally designated 23. Shaft 24 rotates withshaft 22 through clutch portion 25, or is idle when the clutch-brakeassembly 23 is stopped against its brake portion 26. Drive gear 27 isfast upon shaft 24, and is in mesh with gear 28, which, in turn, is fastupon the end of input shaft 29. It will be observed that input shaft 29extends across the entire width of the apparatus, and is appropriatelyjournaled for rotation with suitable hearings in each of the uprightpost members 12-17 inclusive.

At opposite ends of the input shaft 29, there are disposed driver unitssuch as the driver units generally designated 30 and 31, these being ofthe rack-andpinion type. With particular attention being directed toFIGS. 1 and 2 of the drawings, a crank element is secured to each end ofthe shaft 29, such as the crank elements 33 and 34, each comprising acomponent part of drivers 30 and 31 respectively. Each of the cranks 33and 34 is provided with a screw adjustment such as the screw adjustmentcolumn 36 for radially adjusting the respective crank pins, such as thepin 37 at a desired radial distance from the axis of shaft 29. A gearrack 28 is pivotally secured to pin 37 and a similar gear rack 39 ispivotally secured to pin 40 which is a portion of driver 31. At eachside of the machine, a rack guide such as the rack guide 41 is provided,along with a pinion gear 42 (illustrated in detail in FIG. 5) which isalternately driven in one direction and then in the other during therotation of input shaft 29 and its respective cranks. Each of thepinions 42 is secured fast onto shafts such as the respective shafts 44and 45, these shafts being provided with gearing 46 and 47 respectively.Gears 46 and 47 drive pinions 48 and 49 secured to shafts 50 and 51respectively, shafts 50 and 51 being 10 journaled in parallelrelationship to shafts 44 and 45.

Also secured to each of the shafts and 51 are gears 52 and 53respectively, which, in turn, drive gears 54 and 55 which are secured tosleeves 56 and 57, sleeve 56 being journaled across frame members 16 and17, sleeve 57 being journaled across frame members 12 and 13. Sleeve 56is secured to clutch-brake assembly 60, while sleeve 57 is coupled toclutch-brake assembly 61. As is apparent in the drawing, sleeve 56 iscoupled to clutch member 62 in clutch-brake assembly 60, while sleeve 57is secured to clutch member 63 in clutch-brake assembly 61. The core 64in clutch-brake assembly is operatively coupled through an overridingclutch assembly 65a to one end of the draw roll drive shaft 65 whilecore 66 of clutch-brake assembly 61 is operatively coupled through anoverriding clutch assembly 670 to draw roll drive shaft 67 at the otherside. Brake 68 in clutch-brake assembly 60, as well as brake 69 inclutch-brake assembly 61, are each adapted to hold the draw roll shaftstationary until either of the clutch members 62 or 63 is energized,whereupon the draw roll or output shaft 70 will rotate with either ofthe drivers 30 or 31 through the overriding clutches 65a 0r 67arespectively. (See FIG. 8 for details of this portion of the structure.)Thus, the draw roll shaft is initially energized by one of the drivers,for example, driver 30 through its overriding clutch 65a, and at itspoint in the driving cycle where its arcuate rate of speed deceleratesto match the accelerating rate of speed of driver 31, driver 31 willcontrol the delivery of motion to the draw roll through its overridingclutch 67a. Thus, the clutch-brake assemblies may be simultaneouslyenergized, and phased driving of the assemblies occurs without the needof an electrical flip-flop circuit. The overriding clutch assemblies areaccordingly utilized as a replacement for the flip-flop circuits whichwould otherwise be required.

The use of a pair of racks on opposite sides of the draw roll enhancethe dynamic balance of the apparatus, however it will be appreciated, ofcourse, that both driver mechanisms may be provided on only one side orthe other of the structure. Also, in addition to rack and piniondevices, Geneva drives or stepping motors may be employed.

Draw roll 70, which is the output shaft of the structure, is suitablyjournaled in bearings within frame posts 14 and 15, and is arranged inparallel relationship with a mating roll 71, disposed immediatelythereabove. Roll 71 is, of course, journaled in axial parallelrelationship or alignment with roll 70, and is preferably slidablymounted at each side of the apparatus in posts 14 and 15 respectively.Means are provided for permitting the upper roll 71 to be disposed inpressure engagement with the draw roll or output shaft 70.

It is preferable that a resilient sleeve surround each of the shafts 70and 71, as shown in FIG. 7, such as the resilient sleeves 73 and 74.These resilient sleeves are preferably provided with a series of axiallyspaced circumferential slots such as the slotted area 75, each slotbeing adapted to retain a finger 76, as shown in FIG. 7. The fingerseach preferably terminate in a forwardly bent portion and prevent webmaterial from clinging to the drive rolls and becoming wrappedtherearound.

Another axially aligned roll assembly 80 lies parallel to the rollsections 70 and 71 as shown in FIG. 7, and is also rotatably journaledfor rotation on shaft 81 across frame elements 14 and to permitindependent rotation thereof. A further roll assembly 82 is journaled onshaft 83 which is on substantially the same plane as shaft 81, and isprovided with means journaling the shaft for rotation within the framemembers 14 and 15.

A synchronizing roll assembly 84 is also provided and arranged in axialalignment with the other roll assemblies. Shaft 84 is mounted forrotation within a pair of spaced blocks 8585, these spaced blocks beingthreadedly mounted upon a vertical screw rod 86 which is mounted forrotation between spaced brackets at the upper portion of each of theframe posts 14 and 15. Handle element 87 is used to control the motionof the screw rod 86, and if desired, a worm drive arrangement as shownat 88 and 89 may be used to drivably in ter-connect a pair of oppositelydisposed screw rods 86. The details of this structure are discussed inUS. Pat. No. 2,947,345 referred to hereinabove.

Also in alignment with draw rolls 70 and 71 is a backup paid roll 91 forcutting and sealing webs. Roll 91 is tough and resistant to heat, and ispreferably provided with an exterior layer of polytetrafluoroethylene(Teflon). The upper surface of roll 91 is substantially on thehorizontal plane with the nip of the rolls 70 and 71, with the web 92being arranged to pass thereover. The cutting and sealing roll 91 has acentral shaft 93 which is journaled in the frame elements 14 and 15, andpreferably has an axial extension to which sprocket 93a is secured.Sprocket 93a is drivably inter-connected with sprocket 94 by means ofroller chain 95. Thus, whenever draw roll 70 rotates, the cutting andsealing roll 91 will also rotate in the same direction. Since the roll91 must rotate sufficiently fast to accommodate web travel, it ispreferable to move the sealing roll at a somewhat more rapid peripheralrate of speed than the web speed so as to eliminate wrinkle or bucklingof the web.

Forwardly of the cutting and sealing roll 91 is an endless delivery beltassembly 102 which is trained about roller means 103 to pick off severedand sealed articles from the roll 91 as shown in FIG. 7. A rocking frame104 is pivotally mounted at 105 just above the upper stretch of belt 102and carries a pick-off roller 106 normally biased out of contact withbelt 102 but depressible at the end of cutting and sealing of an articleso as to pull it away from the roll 91 and cause it to travel on belt102, the individual articles may be disposed of in a manner common inthe art, such as by stacking, or the like. The details of actuation ofsolenoid 108 are described in US Pat. No. 2,947,345.

If desired, the web advancing may be controlled by an electric eyecontrol system similar to that described in detail in US. Pat. No.2,947,345, and also in other techniques well known in the art. In thisevent, however, the termination of coupling of driver 31 throughclutch-brake assembly 61 will control the ultimate length of draw, withthe initiation of the draw cycle being determined by driver 30.

CUTTING AND SEALING OPERATION In order to properly cut and seal the web92, a single straight hot knife blade overlies the cutting and sealingroll 91 normally in spaced relation and is adapted to be depressedthereagainst when the superimposed webs forming web 92 have beenadvanced to their proper positions on roll 91. Hot knife 115 is heatedto a constant temperature through electric leads 116 from a controlledsource of energy, not shown. Hot knife 115 has a latticed frame mounting117 so constructed as not to permit accumulation of heat or thedevelopment of unevenly heated areas along the length of the blade 115.The knife 115 is caused to slide vertically with respect to frameelements 14 and 15 and in guided relation therewith. The frame 117 iseccentrically mounted at a side of the machine to a pivot block 118, thepivot block 118, in turn, being secured to a shaft 119, as shown in FIG.6. A handle is secured forwardly on each of the pivot blocks 118 sothat, when either handle 120 is raised, the knife 115 will be keptupwardly in spaced relation with the roll 91 at all timesv The shaft 119is rotatably mounted adjacent each end in arm 122, the latter beingpivotally suspended at 123 from a link 124, in turn pivotally mounted ata fixed position 125 at corresponding sides of the frame elements 14 and15. On each of the arms 122 between the pivot points 119 and 123 ispivotally secured at 126 a depending yoke 127 which, in turn, ridesloosely upon an eccentric 128, as shown in FIG. 6. Eccentrics 128 aresecured in the same relative position to a shaft 129 which extendsacross the frame elements 14 and 15 and operates simultaneously. A crankarm 130 is secured to shaft 129 so that, whenever the crank 130 issecured to shaft 129 so that, Whenever the crank 130 is movedcounter-clockwise for a short distance, the yoke 127 will be permittedto lower at each position and will permit the knife 115 to descendtoward the roll 91. If the handles 120 are in lower position, the hotknife 115 will actually contact the roll 91 and press thereagainst Withits own weight suspended thereon. Bearing pressure will then be removedfrom each of the yokes 127 and its corresponding eccentric 128. Inpractice, a small clearance such as one-sixteenth on an inch issufficient to permit the knife blade 115 to rest its weight upon roll 91without being forced downwardly thereagainst.

The crank 130 is actuated by a piston rod 131 which is pivotallyconnected thereto at 132. The piston rod 131, in turn, is connected to apiston 133 which is slidably received within the hydraulic cylinder 134.A compression spring 135 biases the piston 133 normally rearward so asto maintain the crank 130 rearward and the knife blade 115 in raisedposition. Cylinder 134 is rigidly mounted to a bracket 136 which, inturn, is secured to frame elements 14 and 15. A hydraulic inlet tube 137communicates with the rear end of the cylinder 134 for causing thepiston to move forwardly against compression spring 135. Upon release ofpressure, the spring 135 will cause the piston to return and force fluidoutwardly through the tube 137. An adjustably abutment screw 138 isthreadably mounted in the rear end 139 of the cylinder 134 and has athumb nut 140 at the outer end thereof for adjusting the abutment stop141, which, in turn, determines the rearmost position of piston 133under biasing influence of compression spring 135. Another nut 142 hasan annular groove 143 which is adapted to slidably receive a yoke 144 asshown in FIG. 6. The yoke 144 extends forwardly in bracketed slidingengagement with the cylinder 134 and has mounted thereon a switch 145which is operated by an actuator 146 having a bifurcated forward end 147and normally biased forwardly by compression spring 148. Crank arm 130carries a pin 149 which is received in the bifurcated portion 147 of theswitch actuator 146. When the arm 130 and piston 133 are biasedrearwardly, the switch 145 will establish one circuit while, when movedforwardly under the pressure of hydraulic fluid in line 137, willestablish another circuit, as will be described in detail under'theoperation of the machine.

ELECTRICAL CIRCUIT AND OPERATION In order to establish a side-weldingoperation for the preparation of bags or other elongated structures fromthe web 92, the web is initially positioned on the roll system, with thefolded web being advanced by the output shaft operating the draw rolls70 and 71. The hot knife 115 will be maintained at a constanttemperature suitable for-cutting and welding the particularthermoplastic web in the desired thickness. The main drive motor 20 isconstantly energized and rotates the input shaft 29 through gears 27 and28 whenever clutchbrake assembly 23 is energized, it being understoodthat no rotation is imparted to input shaft 29 when clutch 25 isde-energized and brake 26 is energized. Cams 150, 151, 152 and 153 areall fixed to, and rotate with shaft 29 to establish the sequence ofoperation.

In operation, an operational cycle of the apparatus includes onecomplete rotation of input shaft 29 beginning with the individual crankarms 33 and 34 in out-ofphase alignment, but with the crank arm 33 inupright position and in alignment with the gear rack 38. Thus, theposition illustrated in FIG. 1 is subsequent to this point in the cycle,with the crank arms having progressed a short arcuate distance from thestarting point. The individual crank arms are disposed 120 from eachother, with the arm 33 leading the arm 34. Energization of clutches 62and 63 may occur simultaneously with the commencement of the draw cycle,and with clutch 62 being dominant in the beginning of the cycle. Withattention being directed to FIG. 3 of the drawings, it will be observedthat the rate of motion of the web increases until a peak or top speedis reached at 90 of motion of the input shaft 29, and thereafter therate decreases on a sinusoidal rate until 150 of motion has beenachieved. At that point, clutch 63 continues to be energized so as tobecome dominant and couple driver 31 to the output shaft 70 throughoverriding clutch 67a, thus constituting the draw roll of the system.The driver 31 controls the motion for the portion of the cycle between150 and 300 of rotation of the input shaft 29. The remaining 60 areutilized for dwell, during which the sealing operation will occur. Withthis arrangement, long bag structures, up to 30 inches or more inlength, may be fabricated at rapid machine rates. The peak speed for a30-inch bag compares to that for an 18-inch bag fabricated by machinesutilizing conventional draw cycles extending for only 180 of rotation.

In this normal operational mode, cam wheel 150 controls the clutch-brakesystem 23, and cam wheel 153 controls the clutch-brake systems 60 and 61which in turn drive and retain the output shaft or draw roll 70. Camwheel 151 initiates the cutting and sealing movement of hot knife and atiming cycle which determines the dwell period thereof. Cam wheel 152 isutilized to control the operation of an electric eye in the system; whenutilized.

The operation of the circuitry is set forth in detail in US. Pat. No.2,947,345, and reference is made to that disclosure for the details ofoperation of the present structure, it being understood that the presentarrangement is for a single web rather than a dual web as discussed inUS. Pat. No. 2,947,345, and further that the clutch assemblies 62 and 63are normally simultaneously energized for the entire draw cycle andsimultaneously de-energized during the dwell cycle.

It will be appreciated, also, that the operation of cam wheels and 153is closely coordinated and controlled in order that the actuation occurson a smooth basis, thus eliminating any tendency for the film to beabruptly jerked during the draw cycle.

Typically, in the normal operational mode, the extent of overlap of theindividual drive cycles for the drivers 30 and 31 will be equal to thelength of the dwell. Since 60 dwell is typical, a 60 overlap is normallyemployed, thus providing for the 120 phase shift. It will be appreciatedthat the modest ripple which occurs or appears in the draw cycle is lesssevere for the web than the rigorous treatment previously afforded byconventional units utilizing draws. The apparatus of the presentinvention has been found capable of producing bags 31 inches in lengthat a cycle rate of 120 cycles per minute. Also, in a typical operationalcycle of this type, the dwell cycle includes 80 of timing, with 30 ofthe dwell time being devoted to the actual sealing operation. Theremaining 50 of dwell are utilized with one-half being devoted to alowering of the knife, and one-half being utilized for the raising ofthe knife. Longer knife dwell times may be utilized for some sealingoperations, such as for periods of up to at least 54. At a sealing rateof 50 of dwell and for l /2 mil polyethylene, a bar temper ature of 800F. is employed, while temperatures ranging from between 750 and 850 F.may be found satisfactory. The conveyor speed for the output is held ormaintained at a rate of 400 feet per minute, with rates from 350 feetper minute to 400 feet per minute being typical.

It will be appreciated that the times and temperatures set forthhereinabove, are typical of certain operational modes. It is possible,therefore, to utilize lower temperatures with longer dwell times andsatisfactory seals are still obtained. In one operation, it has beenfound that l /2 mil polyethylene may be sealed with a sealing bar havinga temperature of 300 F., however the dwell time is 30 of a 90 cycle perminute rate. It will also be appreciated that side-weld and bottom sealsmay be prepared utilizing this mechanism.

The utilization of one-way or overriding clutches inthe drive mechanismhas been found to provide smooth mechanical switch-over from one inputto the other, and any anomolies which occur in mechanical switching willnotadversely affect performance. This is help ful in certain cases withwebbing which could be adversely affected by abrupt changes in rates ofspeed of draw.

I claim:

1. Means for intermittently advancing a web of flexible film comprising:

a. drive means for imparting repeating cycles of intermittent motion anddwell to said web with the motion normally being along a certainpredetermined web direction; said drive means including output shaftmeans having first and second input driver means operatively coupledthereto;

b. input shaft means and means for drivably rotating said input shaft inone rotational direction;

c. unitary output shaft means adapted to be operatively coupled to saidweb for imparting motion thereto;

d. first and second driver means arranged in phased relationshipone-to-another and being responsive to the rotation of said input shaftmeans and operatively coupled to said output shaft for drivably rotatingsaid output shaft in one rotational direction, each driver means beingeffective for the rotation of said output shaft for a driving cycle ofsaid output shaft, with continuously varying rates of rotationalvelocity having acceleration from dwell to maximum velocity anddeceleration from maximum velocity to dwell, and further being effectiveonly during one-half of each rotational cycle imparted to each of saiddriver means by said input shaft;

e. means including first unidirectional clutch means inter-coupling saidfirst driver means to said input and output shafts for initiatingrotation of said out put shaft and for continuing said rotation for afirst motion segment not exceeding one-half cycle of rotation of saidinput shaft and for de-coupling said first driver means at the end ofsaid first motion segment;

f. means including second unidirectional clutch means for intermittentlyinter-coupling said second driver means to said input and output shaftsin phased relationship to said first driver means and for achievingover-riding de-coupling of said first driver means from said outputshaft for continuing rotation of said output shaft for a second motionsegment not exceeding one-half cycle of rotation of said input shaft andfor de-coupling said second driver means upon completion of said secondmotion segment; and

g. means for maintaining said output shaft means in locked dispositionwhile said first driver means and said second driver means aresimultaneously decoupled from said output shaft to impart a dwell cycleto said web.

2. The apparatus as defined in claim 1 being particularly characterizedin that said first and second motion segments are substantially equal.

3. The apparatus as defined in claim 1 being particularly characterizedin that said first and second driver means are arranged in phasedrelationship one-toanother by an arcuate distance of less than 180.

4. The apparatus as defined in claim 1 being particularly characterizedin that brake means are coupled to said output shaft means, and meansare provided for energizing said brake means for that dwell portion ofthe cycle remaining after termination of said first and said secondmotion segments.

5. The apparatus as defined in claim 1 being particularly characterizedin that said first and second driver means are in phased relationship,one-to-another by an arcuate distance of between 45 and 165.

6. The apparatus as defined in claim 1 being particularly characterizedin that said first and second driver means are rack-and-pinion drivers.

7'. The apparatus as defined in claim 6 being particularly characterizedin that said rack-and-pinion driver means are disposed on opposite endsof 'said input and output shafts.

8. Thermoplastic web treating apparatus comprising, in combination,drive means for intermittently advancing superimposed webs ofthermoplastic sheet film material and for stopping said superimposedwebs for a pre-determined period of dwell, and hot knife means forthermally welding said superimposed webs together at predeterminedspaced intervals therealong, said drive means comprising:

a. drive means for imparting repeating cycles of intermittent motion anddwell to said web with the motion normally being along a certainpre-determined web direction, said drive means including output shaftmeans having first and second input driver means operatively coupledthereto;

b. input shaft means and means for drivably rotating said input shaft inone rotational direction;

c. unitary output shaft means adapted to be operatively coupled to saidweb for imparting motion thereto;

d. first and second driver means arranged in phased relationshipone-to-another and being responsive to the rotation of said input shaftmeans and operatively coupled to said output shaft for drivably rotatingsaid output shaft in one rotational direction, each driver means beingeffective for the rotation of said output shaft for a driving cycle ofsaid output shaft, with continuously varying rates of rotationalvelocity having acceleration from dwell to maximum velocity anddeceleration from maximum velocity to dwell, and further being effectiveonly during one-half of each rotational cycle imparted to each of saiddriver means by said input shaft;

e. means including first unidirectional clutch means inter-coupling saidfirst driver means to said input and output shafts for initiatingrotation of said output shaft and for continuing said rotation for afirst motion segment not exceeding one-half cycle of rotation of saidinput shaft and for de-coupling said first driver means at the end ofsaid first motion segment;

f. means including second unidirectional clutch means for intermittentlyinter-coupling said second driver means to said input and output shaftsin phased relationship to said first driver means and for achievingover-riding de-coupling of said first driver means from said outputshaft for continuing rotation of said output shaft for a second motionsegment not exceeding one-half cycle of rotation of said input shaft andfor de-coupling said second driver means upon completion of said secondmotion segment;

g. means for maintaining said output shaft means in locked dispositionwhile said first driver means and said second driver means aresimultaneously decoupled from said output shaft to impart a dwell cycleto said web; and

saidhot knife means comprising:

h. heated blade means disposed generally transversely of the web axisand normally spaced from said web axis during advance of the web, andmeans for reciprocably moving said blade relative to said web to bringsaid blade into contact with adapted to move reciprocably toward andaway from said superimposed webs, and into contact with said webs.

UNITED STATES PATENT OFFICE QETEFICATE 0F CORRECTIQN PATENT NO. I3,884,129 DATED May 20, 1975 INVENTOR(S) Thomas J. Monahan It iscertified that error appears in the ab0ve-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, line 64, "gear rack 28" should read gear rack 38 Column 6,lines 34 and 35, delete the repeated phrase "the crank 130 is secured toshaft 129 so that, whenever" Baigncd and Sealed this Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uflalenlsand Trademarks

1. Means for intermittently advancing a web of flexible film comprising:a. drive means for imparting repeating cycles of intermittent motion anddwell to said web with the motion normally being along a certainpredetermined web direction, said drive means including output shaftmeans having first and second input driver means operatively coupledthereto; b. input shaft means and means for drivably rotating said inputshaft in one rotational direction; c. unitary output shaft means adaptedto be operatively coupled to said web for imparting motion thereto; d.first and second driver means arranged in phased relationshipone-to-another and being responsive to the rotation of said input shaftmeans and operatively coupled to said output shaft for drivably rotatingsaid output shaft in one rotational direction, each driver means beingeffective for the rotation of said output shaft for a driving cycle ofsaid output shaft, with continuously varying rates of rotationalvelocity having acceleration from dwell to maximum velocity anddeceleration from maximum velocity to dwell, and further being effectiveonly during one-half of each rotational cycle imparted to each of saiddriver means by said input shaft; e. means including firstunidirectional clutch means intercoupling said first driver means tosaid input and output shafts for initiating rotation of said outputshaft and for continuing said rotation for a first motion segment notexceeding one-half cycle of rotation of said input shaft and forde-coupling said first driver means at the end of said first motionsegment; f. means including second unidirectional clutch means forintermittently inter-coupling said second driVer means to said input andoutput shafts in phased relationship to said first driver means and forachieving over-riding de-coupling of said first driver means from saidoutput shaft for continuing rotation of said output shaft for a secondmotion segment not exceeding one-half cycle of rotation of said inputshaft and for de-coupling said second driver means upon completion ofsaid second motion segment; and g. means for maintaining said outputshaft means in locked disposition while said first driver means and saidsecond driver means are simultaneously de-coupled from said output shaftto impart a dwell cycle to said web.
 2. The apparatus as defined inclaim 1 being particularly characterized in that said first and secondmotion segments are substantially equal.
 3. The apparatus as defined inclaim 1 being particularly characterized in that said first and seconddriver means are arranged in phased relationship one-to-another by anarcuate distance of less than 180*.
 4. The apparatus as defined in claim1 being particularly characterized in that brake means are coupled tosaid output shaft means, and means are provided for energizing saidbrake means for that dwell portion of the cycle remaining aftertermination of said first and said second motion segments.
 5. Theapparatus as defined in claim 1 being particularly characterized in thatsaid first and second driver means are in phased relationship,one-to-another by an arcuate distance of between 45* and 165*.
 6. Theapparatus as defined in claim 1 being particularly characterized in thatsaid first and second driver means are rack-and-pinion drivers.
 7. Theapparatus as defined in claim 6 being particularly characterized in thatsaid rack-and-pinion driver means are disposed on opposite ends of saidinput and output shafts.
 8. Thermoplastic web treating apparatuscomprising, in combination, drive means for intermittently advancingsuperimposed webs of thermoplastic sheet film material and for stoppingsaid superimposed webs for a pre-determined period of dwell, and hotknife means for thermally welding said superimposed webs together atpredetermined spaced intervals therealong, said drive means comprising:a. drive means for imparting repeating cycles of intermittent motion anddwell to said web with the motion normally being along a certainpre-determined web direction, said drive means including output shaftmeans having first and second input driver means operatively coupledthereto; b. input shaft means and means for drivably rotating said inputshaft in one rotational direction; c. unitary output shaft means adaptedto be operatively coupled to said web for imparting motion thereto; d.first and second driver means arranged in phased relationshipone-to-another and being responsive to the rotation of said input shaftmeans and operatively coupled to said output shaft for drivably rotatingsaid output shaft in one rotational direction, each driver means beingeffective for the rotation of said output shaft for a driving cycle ofsaid output shaft, with continuously varying rates of rotationalvelocity having acceleration from dwell to maximum velocity anddeceleration from maximum velocity to dwell, and further being effectiveonly during one-half of each rotational cycle imparted to each of saiddriver means by said input shaft; e. means including firstunidirectional clutch means inter-coupling said first driver means tosaid input and output shafts for initiating rotation of said outputshaft and for continuing said rotation for a first motion segment notexceeding one-half cycle of rotation of said input shaft and forde-coupling said first driver means at the end of said first motionsegment; f. means including second unidirectional clutch means forintermittently inter-coupling said second driver means to said input andoutput shafts in phased relationship to said first driver means and forachieving over-riding de-coUpling of said first driver means from saidoutput shaft for continuing rotation of said output shaft for a secondmotion segment not exceeding one-half cycle of rotation of said inputshaft and for de-coupling said second driver means upon completion ofsaid second motion segment; g. means for maintaining said output shaftmeans in locked disposition while said first driver means and saidsecond driver means are simultaneously de-coupled from said output shaftto impart a dwell cycle to said web; and said hot knife meanscomprising: h. heated blade means disposed generally transversely of theweb axis and normally spaced from said web axis during advance of theweb, and means for reciprocably moving said blade relative to said webto bring said blade into contact with said superimposed webs for weldingsaid webs together during said period of dwell.
 9. The combination asdefined in claim 8 being particularly characterized in that said hotknife means is adapted to move reciprocably toward and away from saidsuperimposed webs, and into contact with said webs.